Stabilized alkoxy aromatic amines



Patented Oct. 12, 1954 UNITED STATES TENT OFFICE STABILIZED ALKOXY AROMATIC AMINES No Dra-wing. Application May 1, 1952, Serial No. 285,547

19 Claims. 1

This invention relates to alkoxy substituted aromatic amines which have been stabilized. against atmospheric oxidation, particularly by having incorporated therein small proportions of anew class of anti-oxidants therefor.

,It has long been recognized that aromatic amines tend to become rapidly oxidized through contact with air which results in loss of the aromatic amines and decrease in their quality through contamination by the oxidation products. When aromatic amines have acquired a dark color from exposure to air, they are not suitable for the manufacture of azo dyes, pigments, basic colors, vat dyes, pharmaceuticals, mbber chemicals, etc. In practice, such oxidation has been largely avoided by consuming the amines within a few days of their production or the amines have been purified, by distillation or crystallization, just prior to their use. In some cases, the loss of unstabilized amine has been as high as 1% per week and the accumulated oxidation products have adversely afiected the yield of substances prepared therefrom, such as azo dyes, by as much as 10%.

In industrial practice, the close scheduling of the production of the amines with the processes in which the amines are consumed has become increasingly less practical. The storage of amines, which deteriorate so that they require purification before use, is prohibitively costly because of the loss of amine by oxidation and the further losses incurred in the purification processes.

Attempts to stabilize aromatic amines, by the use of conventional anti-oxidants employed for stabilizing other substances, have not been commercially successful because such anti-oxidants are inefficient or inoperative. In many cases, such conventional anti-oxidants produce negative results in the aromatic amines; that is, they act as pro-oxygenic catalysts. Also, most metal deactivating agents actually increase the susceptibility of the aromatic amines to attack by atmospheric oxygen.

A. E. Robertson, in Patent No. 233M551, proposes to stabilize aromatic amines 'by adding carbon .bisulfide thereto, which carbon bisulfide tends to liberate hydrogen sulfide. While carbon bisulfide and hydrogen sulfide are quite effective anti-oxidants for aromatic amines, they are gases which readily escape from the amines, are obnoxious and toxic and present explosion and corrosion hazards which greatly reduce their utility.

Herbst, in Patent No. 2,422,484, has also proposed the stabilization of certain .alkaryl amines with aromatic mercaptans. However, in general, such aromatic mercaptans are not particularly efiective in such amines and some of them, after a short period, invert .to pro-oxygenic catalysts in such amines. Also, some of such aromatic mercaptans are inoperative with some amines and actually increase the susceptibility of such amines .to atmospheric oxidation.

In my copending application, Serial No. 188,871, filed October '6, 1950, now Patent No. 2,655,543, for Stabilized Aromatic Amines, I have disclosed that certain aromatic amines, other than the. alkoxy substituted aromatic amines of the present invention, can be stabilized .a particular class of heterocyclic compounds. While some of the heterocyclic compounds of such prior application are effective to stabilize the alkoxy substituted aromatic amines of the present invention, others are not, some of them actuallly increasing the susceptibility of the alkoxy substituted aromatic amines to atmospheric oxidation.

It is an object of my invention to provide .a certain class of alkoxy substituted aromatic amines containing a class of compounds which are particularly effective to inhibit oxidation of such amines and which .do not invert to prooxygenic catalysts therein. .Another object is to provide a class of alkoxy substituted aromatic amines which are effectively stabilized against atmospheric oxidation, whereby loss of amine by oxidation is prevented, contamination of the amine by oxidation products is reduced and the deleterious effects of the oxidation products in the amine are avoided. A further object is to provide a novel and improved method of stabilizing a specific class of alkoxy substituted aromatic amines. Further objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with my invention which comprises incorporating in an alkoxy substituted aromatic amine *of the formula R-NHz in which R is-a member of .the group consisting of mono- .lsubstitu-ted phenyl radicals in which the substituent is a alkoxy group of -1 to 2 carbon atoms in one of the :positions ortho and parawto the NI-l2 group and :disubstituted phenyl radicals in which one substituent :is a :methoxy group :in .one of :the positions ortho and para to the .NHz group and the othersubstituent is a methyl group, ,from about 0.0.-1% to about 0.5% .of va member :of the group consisting of heterocyclic compounds and their zinc salts in which each heterocyclic compound contains 2 to 10 carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of to 6 atoms of which 2 to 4 atoms are carbon atoms and 2 to 3 atoms are heterocyclic atoms selected from the group consisting of sulfur and nitrogen atoms, not more than 2 of such heterocyclic atoms being alike, the substituents on all heterocyclic nitrogen atoms being restricted to hydrogen atoms and a single methyl group, and the substituents on the carbon atoms of the heterocyclic ring being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbon radicals, SH and =8, there being no more than one saturated hydrocarbon radical or --SH on any single carbon atom of the heterccyclic ring, Thereby, such alkoxy substituted aromatic amines are effectively stabilized against atmospheric oxidation.

I have found that such heterocyclic compounds and their zinc salts are efiieient antioxidants for such alkoxy substituted aromatic amines. They effectively inhibit oxidation of such amin s and prevent loss of the amine by oxidation, reduce contamination of the amine by oxidation products and avoid the synergistic action of the oxidation products in subsequent chemical processes in which the amines are employed. The resulting stabilized alkoxy substituted aromatic amines may be stored for relatively long periods of time, thereby obviating the necessity for close scheduling of the amine production with the process in which the amine is consumed and usually making costly purification processes unnecessary. Such heterocyclic compounds and their zinc salts are also effective to protect the amines in the processes by which they are manufactured so that higher yields of amine of better quality can be obtained.

The alkoxy aromatic amines, which can be effectively stabilized by the heterocyclic compounds of my invention, are those of the formula RNH2 in which R represents a monosubstituted phenyl radical in which the substituent is an alkoxy group of l to 2 carbon atoms in one of the positions ortho and para to the NHz group, i. e. ortho-anisidine, para-anisidine, orthophenetidine and para-phenetidine; and those of the formula R-NHz in which R represents a disubstituted phenyl radical in which one substituent is a methoxy group in one of the positions ortho and para to the NH: group and the other substituent is a methyl group, i. e. the adjacent homologues of ortho-anisidine and para-anisidine, represented by cresidine (2- methoxy-5-methyl aniline).

The heterocyclic compounds of my invention are those which contain 2 to carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of 5 to 6 atoms of which 2 to 4 atoms are carbon atoms, and 2 to 3 atoms are heterocyclic atoms selected from the group consisting of sulfur and nitrogen atoms, not more than 2 of such heterocyclic atoms being alike, the substituents on any heterocyclic nitrogen atoms being restricted to hydrogen atoms and a single methyl group and the substitutents on the carbon atoms of the heterocyclic ring being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbon radicals, SH and =S, there being no more than one saturated hydrocarbon radical or SI-I on any single carbon atom of the heterocyclic ring, and their zinc salts. Substituent groups, on the carbon atoms of the heterocyclic ring, which contain unsaturated carbon-carbon bonds, including those in benzene rings, tend to result in compounds which are inoperative in at least some of the alkoxy aromatic amines. Also, organic substituents on the acyclic sulfur atoms tend to result in inoperative compounds. By an acyclic sulfur atom, I mean one which is outside the ring. Generally, those compounds, which contain one or more acyclic sulfur atoms, may be designated by either of two or more tautomeric formulae, in at least one of which the acyclic sulfur is bonded to both a hydrogen atom and a carbon atom of the heterocyclic ring, and the designation of any such compound by any one of its tautomeric formulae will be understood to mean such compound with any of its assignable formulae.

Preferred classes of heterocyclic compounds comprise those compounds which consist of 2 to 10 carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 2 to 3 sulfur atoms, and at least 2 hydrogen atoms and contain a single heterocyclic ring of 5 to 6 atoms composed of at least 2 carbon atoms, 1 to 2 nitrogen atoms and 1 to 2 sulfur atoms, the substituents on the nitrogen atoms being restricted to hydrogen atoms, each sulfur atom, other than those that are members of the heterocyclic ring, being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, and, particularly, those which contain only 1 sulfur atom in the ring and 1 to 2 acyclic sulfur atoms bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, and the zinc salts thereof.

Other preferred classes of heterocyclic compounds comprise those compounds which consist of 2 to 6 carbon atoms, 1 to 2 heterocyclic nitro-- gen atoms, 2 to 3 sulfur atoms, and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 to 6 atoms composed of 2 to 3 carbon atoms, 1 to 2 nitrogen atoms, and 1 to 2 sulfur atoms, the substituents on the nitrogen atoms being restricted to hydrogen atoms, each sulfur atom, other than those that are members of the heterocyclic ring, being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, all carboncarbon bonds in the heterocyclic compound being single bonds, and the zinc salts of such compounds.

Representative heterocyclic compounds of my invention are listed below with their formulae, including the tautomeric formulae:

Thiazoline-2-thiol Thiazoline-2-thiol, zinc salt 0 H2 N H Ethylene trithiocarbonate o H?- s 0: s

l-methyl-imidazole-Z-thio CHrCH-CH The concentration of the anti-oxidant in the amine. should be from about" 0201% to, about:

0.5 %'v by weight-preferably; from about 0.04%- to about 0.2% and usually about 011%. While the anti-oxidants of my'invention may be effective in concentrations above 0. 5%, such higher concentrations will generally be objectionable as they would contaminate the amine to an undesirable extent. 0.'0l'% of anti-oxidant will usually show some effect, but such effect will generally be insufiicient for practical purposes.

Not all of the heterocyclic compounds (antioxidants) of my invention are. equally efiective for all of the alkoxy aromatic amines of. my invention. Accordingly, the particular antioxidant and the concentration employed for eachof the alkoxy aromatic amines will be chosen in accord with the degree of stability desired. Also, the choice" of anti-oxidant and the concentration thereof will be, governed by. the

conditions. to which. the alkoxy aromatic, amine. will be exposed, such as.light,.temperature and atmospheric contact. Light. acts asa catalyst for the. oxidation. of the alkoxy aromatic aminesand; hence, ifthe amine is tobe. exposed to light iorany substantial period of time, it will be necessary to materially increase the concentrationof the anti-oxidant. Furthermore, the rate of. oxidation of the alkoxy aromatic amine increases with increase in temperature, so that,

the concentration of the anti-oxidant should be increased when. the amine is to be subjected to temperatures above atmospheric. Furthermore, the rate of oxidation of the alkoxy aromatic aminevaries with variation in the extent of its exposure to air or oxygen and higher concentrations of anti-oxidant will be required" when the amine is to be exposed to air to anymaterial extent. Therefore, it will be understood that the anti-oxidants exhibit their maximum eniciency under storage conditions which involve room temperature or lower temperatures, exclude light, and provide a minimum contact with air or oxygen, asin: closed metal tanks and drums.

In order to. obtain. optimum. stability of: the

amine, I. generally prefer toadd the: hetero,- cyclic' compound to' the alkoxy: aromatic amine as soon as the amine isprepared, particularly; immediately after distillation or during crystallization of the amine. If the amine is distilled, minimum contact thereof with oxygen and maximum stabilization are obtained if the amine is distilled into a receiver containing the antioxidant. However, the application of my'invention is not restricted to freshly prepared-amines,

as the anti-oxidant may be added'to an alkoxy' aromatic amine which has beenpartially' oxi- Also, concentrations below tardi'furthen oxidation of the amine;

facture. of: the amine to; avoid: atmospheric oxizdation: during tsuchimanufactureyto thereby; ob:-

tain-the amine in higher-v yieldsand better qual,-' ity.- added tojthe crude amine,- before-purification of operation.

If I the alkoxyaromatic amine is' liquid at nor 'mal' temperatures; the anti-oxidant may be:

simply? added thereto in; thev desired. concentra:

tion and dissolved therein. Ifathe amine: is a;

solid at atmospheric temperatures, it may be meltedror' dissolved; in an. inert liquid solvent-and the anti-oxidant added to the melted amine orto-thesolution. Also,- if they anti-oxidant is not soluble in the alkoxy aromatic amine to theextent desired, it may beraddedas a solution in a suitable liquid solvent, such as ethanol, isopropyl alcohol. and ether. compounds efiectivelystabilize the alkoxy aromatic: amines inthe presence of inert liquid solvents and diluents.

Examples are given-hereinafter, illustrating the effect of representativeheterocyclic compounds.

of-- my invention in stabilizing representative. alkoxy aromaticaminessome of such examples including tests with other heterocyclic com--- pounds for purposes of comparison. The tests with' liquid-alkoxy aromatic amines were carried out in clear. glassbottlesafilled to'approx-imately .75% of their. capacity with the amine orstabilized amine and exposed to-diffused daylight at roomtemperature. The bottles were cappedbut not sealedairtight. In the absence of practical specific analytical methods for direct determination of, the concentration of. oxidation products. in. thepreliminary stages, the rate of formation of visible color. was adopted as the basis for the determination of anti-oxidant activity. The development of, color follows an orderly sequence which is related-to the extent of. oxidation. In nearly every case, the first visible indication of oxidation is produced by derivatives which impart a. yellow color to the system, followed. byfurther oxidation to red compounds. Final. stages of oxidativedecomposition were evidenced by the appearance of green and. blue components; Although the oxidation follows a complex series of reactions.

and, the constitutions of many of the inter.-.

mediateproductsare unknown, the autocatalyticnatureof the system can be-easily demonstrated.

Evaluation of. antieoxidants, which are effective Similar. results have. been observed in the red. to Therefore, in

blue-green development. stages.- order to establish a commonbasis for quantita:

tive evaluation of, ante-oxidant:efliciency;.the rate of formation. of each of these three. col'or classes, astwell asztotalv visible color formation, was evaluated as: optical. density determined in a Cenco- Sheard-Sanford Photelometer, using blue- (en-- In particular, the anti-oxidant, may be The heterocyclic:

tral Maximum=4l0 millimicrons), green (525 millimicrons) and red (610 millimicrons) filters and no filter. Distilled water was used as the reference standard, and the density expressed as per cent transmission. Experience has shown that the use of aromatic amines, darker than a red-amber color, do not produce satisfactory results in chemical processes. Therefore, when oxidation has progressed toan extent sufiicient to reduce the total transmission below 75%, blue transmission below 20%, green below 60% and red below 95%, the amine is considered'to be unsuitable for use without purification. The sum of the number of days required to reach each of these four values is designated as the index. The anti-oxidant index is obtained by subtracting the index of the unstabilized control sample from the index of the stabilized material. This method minimizes the small variations in oxidation susceptibility exhibited by individual production lots of most amines.

Evaluation of those amines, which are normally solid at room temperature, was carried out somewhat differently. The antioxidant was dissolved in the amine at a temperaturesufiiciently high to maintain a liquid state. The test was then conducted at that temperature, or the solution was permitted to freeze and the test continued at normal temperature. Since light density measurements were not practical, the progress of the oxidation was estimated visually. The amine was considered unsuitable for use when the color change had progressed to a dark red, dark brown, or dark lavender shade. Since a control sample, containing no anti-oxidant, was tested at the same time, personal variations in judgment of color depth largely cancelled out. In order to place these evaluations on the same index basis adopted for liquid amines, the number of days elapsed to the end point was multiplied by four. In several cases, the crystallizing point was used as the criterion of anti-oxidant eflicienoy.

In order to further show the effectiveness of the anti-oxidants of my invention, the ratio of the stability of the stabilized amine to the stability of the unstabilized amine may be calculated by dividing the index of the stabilized amine by the index of the unstabilized amine (control index). This ratio is the stability ratio. This stability ratio expresses the relation of the storage life of the stabilized amine to the storage life of the unstabilized amine under the same conditions. For example, a stability ratio of 2 indicates that the stabilized amine requires twice as long as the unstabilized amine to reach the final stage of oxidative decomposition where it is considered to be unsuitable for most uses; that is, the stabilized amine has a storage life 2 times that of the unstabilized amine.

EXAMPLE 1 Ortho-am'sidine Colorless samples of ortho-anisidine, which had a crystallizing point above 4 C., were obtained by distillation under reduced pressure mm. of mercury) at 101-104 C. Inhibitors were added in the indicated concentrations to 50 cc. aliquots which were then stored at room temperature in clear glass, lightly capped bottles exposed to diffused daylight. Color changes were observed periodically. The results, expressed as antioxidant index, are summarized in the following table:

Anti- Control Wt. Inhlbltor Index Percent 3%;?

Ethylene trithiocarbonate 44 0. 1 64 Thiazoline-Z-thiol 52 0. 1 54 Thiazoline-Z-thiol, zinc salt. 52 0. 1 30 Thialdine 30 (l. 1 56 Imidazoline-Z-thiol 30 0. 1 40 l-Methyl-imidazole-2-thiol 44 0. l 76 1 ,SA-Thiadiazole-Z,5-dithiol 30 O. 1 80 Antioxidant Index Inhibitors P r ent Cyclohexene trithiocarbonate 0. 1 4 Thiazoline-2-thiol, zinc salt 0.1 8 Thialdine 0. 1 l2 Imidazoline-2-thio1 0. l 4 l,3,4-Thiodiazolo-2,5-dithio1 0. l 4

EXAMPLE 3 Cresidine Cresidine (2-methoxy-5-methyl-aniline) was distilled under reduced pressure (8 mm. of mercury) at 113 114: C. to obtain a nearly colorless product for antioxidant evaluation. The inhibitors were added in the quantities required to produce the indicated concentrations at 70- 75 C. and stirred until dissolved. The aliquots were stored at 7Gi2 C. exposed to atmospheric oxygen in clear glass open mouth bottles. The control index was 8. The following results were observed:

Inh'b't Wt d t l l ors on an Percent Index Thialdino 0.1 20 l,3,4-Thiadiazole-2,fi-ditliiol 0. l 36 The protective action of thialdine is further illustrated by an evaluation of final purity after 10 days at 6870 C., from a comparison of the crystallizing points of the untreated control and of the stabilized sample:

. Degrees centigrade Control 50.7 Thialdine (0.1%) treated aliquot 51.3

The difierence in crystallizing points indicates the presence of significant quantities of oxidation products in the unprotected amine.

EXAMPLE 4 Ortho-phenetidine A sample of commercial ortho-phenetidine was redistilled under reduced pressure (10 mm. of mercury) at 104 C. to obtain a colorless product for antioxidant evaluations. Inhibitors were added, in quantities sufiicient to produce a 0.1%

iby weightconcentration, to'50 cc. aliquots which were then stored at room temperature in clear glass bottles. J'Color changes were followed. The control index was "16.

. Antioxidant lnhlbitors Index l-Methyl-hnidazole-Z-thiol i :8 .1,3,4:Tl1iadiaZ0le-2,5-dithi01 i 60 EXAMPLE 1 5 Farm phenetz'dine Samples of commercial para-phenetidine,

which .contained less "than 2% of impurities or amines other'than para -phenetidine, were distilled underreduced pressure 'mm. of "mercury) at 125C. to obtain a nearly colorless product for'evaluation of oxidation; inhibitors. Antioxidants were incorporated, in "the indicated amounts, to 50 cc. aliquots which werethen-stored at room temperature, and the 'color development followed. The results are .summari'zed-intabula-r form. The control index was 20.

Antioxi- Inhibitor wgf dent .Index Ethylene trithiocarbonate 0.1 72 Cyolohexenev trithiocarbonate 0. 1 1 28 Thiazoline-Z-thiol, zinc salt 0.1 Thialdine 0; 1 108 aromatic amines as disclosed in'my prior copending application Serial No. 188,871 hereinbefore referred to.

It will be understood that thepreceding examples are given-solely for illustrativegpurposes and that'I do notintendpto limit my invention to the specific embodiments disclosedtherein. It will be apparent to those skilled in the art that other alkoxy substituted aromatic amines,within the class heretofore disclosed, may lbe similarly stabilized. It will also .;be apparent that other heterocyclic compounds. and their zinc salts within the classhereinbefore defined, and mixtures of any two or more thereof-maybe substituted .for those of the examples. It will 'befurther apparent that vthe concentration of the antioxidant in the alkoxy aromatic'amine'may also'be varied within .the limitsdisclosed. Still further, the stabilized amine may bediluted with inert liquid solvents.

;It:will .be 'apparent'thah-by-my invention, 1- am able to provide a class of al-koxy'substituted aromatic amines which "are efiectively stabilized against oxidationfor relatively long-periods of time. -"Thereby,-the -amines may bestored without material loss in 'amineor contamination-of consumed as rapidly as they are produced. Also, the losses, entailed in purification of oxidized amine, are eliminated-or greatly reduced. Ac-

cordingly, it is apparent that my invention constitutes a valuable advance in and contribution to "the art.

1..A composition consisting essentially of an aromaticamineof the formula R-NH2 in which Ris a: member of the group consisting of monosubstituted phenyl radicals in which the substituentis an alkoxy group of 1 to 2 carbon atoms in one of .the positions ortho and para to the Ni-I2 group and disubstituted phenyl radicals in which one substituent is a methoxy' group in one of the positions ortho and para to the N112 group :and the other substituent is a methyl group, and from about 001% toabout 0.5% of a member of the group consisting of heterocyclic compounds and theirzinc salts inwhich each'heterocyclic compound contains 2 to 10 carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of 5 to 6 atoms of-which 2 to 4 atoms are carbon atoms and 2 to 3.-atoms are heterocyclic atoms selected from the group consisting of sulfur and nitrogen atoms, notmore than 20f such heterocyclic atoms being alike, the substituents on all heterocyclic nitrogen atoms being restricted to hydrogen atoms and a singlemethyl group, and the substituents on each carbon atom of the heterocyclic ring being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbonradicals, SI-I and =S, there being no'more than one saturated hydrocarbon radical or --SH on any single carbon atom of the heterocyclic ring,

2. A composition consisting essentially of an aromatic amine of the formula R-NH2 in which R is amember of the group consisting of monosubstituted phenyl radicals in which the substituent is an alkoxy group of 1 to 2 carbon atoms inone of the positions ortho and para to the Nl-Iz group and disubstituted phenyl radicals in which one substituent is a-methoxy group in one of the positions ortho and para to the NI-Iz group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of a heterocyclic compound which contains 2 to 10 carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of 5 to 6 atoms of which 2 to 4 atoms are carbon atoms and 2 to 3 atoms are heterocyclicatoms selected from the group consisting of sulfur and nitrogen atoms, not more than2 of such heterocyclic atoms being alike, the substituents on all heterocyclic nitrogen atoms beingrestricted to hydrogen atoms and a single methyl group, and the substituents on the canbon atoms of the heterocyclic ring being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbon-radicals, ---SH and :S, there being no more" than one saturated hydrocarbon radical or -SI-I on any single carbon atom of the heterocyclic ring.

3. A composition consisting essentially of an aromatic amine of the formula RNH2 inwhich R is a member of the group consisting of monosubstituted phenyl radicals in which the substituent is analkoxy group of l to 2 carbon atoms invoneof the positionsortho and para to the NH; .groupand .disubstituted phenyl radicalsin which one substituent is a methoxy group in one of the positions ortho and para to the NH; group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of a heterocyclic compound which consists of 2 to 10 carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 2 to 3 sulfur atoms, and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 to 6 atoms composed of at least 2 carbon atoms, 1 to 2 nitrogen atoms and 1 to 2 sulfur atoms, the substituents on the nitrogen atoms being restricted to hydrogen atoms, each sulfur atom, other than those that are members of the heterocyclic ring, being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, there being no more than one saturated hydrocarbon radical or SH on any single carbon atom of the heterocyclic ring.

4. A composition consisting essentially of an aromatic amine of the formula R-NI-Iz in which R is a member of the group consisting of monosubstituted phenyl radicals in which the substituent is an alkoxy group of l to 2 carbon atoms in one of the positions ortho and para to the Nl-I: group and disubstituted phenyl radicals in which one substituent is a methoxy group in one or" the positions ortho and para to the NI-Iz group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of a heterocyclic compound which consists of 2 to 6 carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 2 to 3 sulfur atoms, and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 to 6 atoms composed of 2 to 3 carbon atoms, and 1 to 2 nitrogen atoms and 1 to 2 sulfur atoms, the substituents on the nitrogen atoms being restricted to hydrogen atoms, each sulfur atom, other than those that are members of the heterocyclic ring, being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, there being no more than one saturated hydrocarbon radical or SH on any single carbon atom of the heterocyclic ring, and all carbon-carbon bonds in the heterocyclic compound being single bonds.

5. A composition consisting essentially of an aromatic amine of the formula RNH2 in which R is a member of the group consisting of monosubstituted phenyl radicals in which the substituent is an alkoxy group of l to 2 carbon atoms in one of the positions ortho and para to the Nl-lz group and disubstituted phenyl radicals in which one substituent is a methoxy group in one of the positions ortho and para to the Nile group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of a heterocyclic compound which consists of 2 to carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 2 to 3 sulfur atoms, and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 to 6 atoms composed of at least 2 carbon atoms, 1 to 2 nitrogen atoms and 1 sulfur atom, the substituents on the nitrogen atoms being restricted to hydrogen atoms, and l to 2 of the sulfur atoms being acyclic sulfur atoms bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, there being no more than one saturated hydrocarbon radical or all on any single carbon atom of the heterocyclic ring.

5. A composition consisting essentially of an aromatic amine oi the formula R-NI-Iz in which R is a member of the group consisting of monosubstituted phenyl radicals in which the substituent is an alkoxy group of l to 2 carbon atoms in one of the positions ortho and para to the NI-Iz group and disubstituted phenyl radicals in which one substituent is a methoxy group in one of the positions ortho and para to the NHz group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of a heterocyclic compound which consists of 2 to 3 carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 1 heterocyclic sulfur atom, 1 to 2 acyclic sulfur atoms and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 atoms composed of 2 to 3 carbon atoms, the 1 to 2 heterocyclic nitrogen atoms and the 1 heterocyclic sulfur atom, the 1 to 2 acyclic sulfur atoms being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, there being no more than one Sl-I on any single carbon atom of the heterocyclic ring, and all carbon-carbon bonds in the heterocyclic compound being single bonds.

'7. A composition consisting essentially of an aromatic amine of the formula RNH2 in which R, is a member of the group consisting of monosubstituted phenyl radicals in which the substituent is an alkoxy group of 1 to 2 carbon atoms in one of the positions ortho and para to the NH: group and disubstituted phenyl radicals in which one substituent is a methoxy group in one of the positions ortho and para to the NI-Iz group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of 1,3,4-thiadiazole- 2,5-dithiol.

8. A composition consisting essentially of an aromatic amine of the formula RNH2 in which R is a member of the group consisting of monosubstituted phenyl radicals in which the substituent is an alkoxy group of 1 to 2 carbon atoms in one of the positions ortho and para to the N112 group and disubstituted phenyl radicals in which one substituent is a methoxy group in one of the positions ortho and para to the N'Hz group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of thiazoline-2- thiol.

9. A composition consisting essentially of an aromatic amine of the formula R-NI-Iz in which R is a mono-alkoxy substituted phenyl radical in which the alkoxy group contains 1 to 2 carbon atoms and is in one of the positions ortho and para to the NHz group, and from about 0.01% to about 0.5% of a member of the group consisting of heterocyclic compounds and their zinc salts in which each heterocyclic compound contains 2 to 10 carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of 5 to 6 atoms of which 2 to 4 atoms are carbon atoms and 2 to 3 atoms are heterocyclic atoms selected from the group consisting of sulfur and nitrogen atoms, not more than 2 of such heterocyclic atoms being alike, the substituents on all heterocyclic nitrogen atoms being restricted to hydrogen atoms and a single methyl group, and the substituents on each carbon atom of the heterocyclic ring being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbon radicals, Sl-I and :8, there being no more than one saturated hydrocarbon radical or -SH on any single carbon atom of the heterocyclic ring.

10. A composition consisting essentially of an aromatic amino of the formula R-NH2 in which R. is a mono-alkoxy substituted phenyl radical in which the alkoxy group contains 1 to 2 carbon atoms and is in one of the positions ortho and para to the NI-Iz group, and from about 0.01%

to about 0.5% of a heterocyclic compound which contains 2 to 10 carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of to 6 atoms of which 2 to 4 atoms are carbon atoms and 2 to 3 atoms are heterocyclic atoms selected from the group consisting of sulfur and nitrogen atoms, not more than 2 of such heterocyclic atoms being alike, the substituents on all heterocyclic nitrogen atoms being restricted to hydrogen atoms and a single methyl group, and the substituents on the carbon atoms of the heterocyclic ring being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbon radicals, -S-l-1 and :8, there being no more than one saturated hydrocarbon radical or -SH on any single carbon atom of the heterocyclic ring.

11. A composition consisting essentially of an aromatic amine of the formula R-NH2 in which R is a monoalkoxy substituted phenyl radical in which the alkoxy group contains 1 to 2 carbon atoms and is in one of the positions ortho and para to the NI-Iz group, and from about 0.01% to about 0.5% of a heterocyclic compound which consists of 2 to carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 2 to 3 sulfur atoms, and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 to 6 atoms composed of at least 2 carbon atoms, 1 to 2 nitrogen atoms and 1 to 2 sulfur atoms, the substituents on the nitrogen atoms being restricted to hydrogen atoms, each sulfur atom, other than those that are members of the heterocyclic ring, being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, there being no more than one saturated hydrocarbon radical or -SH on any single carbon atom of the heterocyclic ring.

12. A composition consisting essentially of an aromatic amine of the formula R-NI-Iz in which R is a monoalkoxy substituted phenyl radical in which the alkoxy group contains 1 to 2 carbon atoms and is in one of the positions ortho and para to the NI-Iz group, and from about 0.01% to about 0.5% of a heterocyclic compound which consists of 2 to 3 carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 1 heterocyclic sulfur atom, 1 to 2 acyclic sulfur atoms and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 atoms composed of 2 to 3 carbon atoms, the 1 to 2 heterocyclic nitrogen atoms and the 1 heterocyclic sulfur atom, the 1 to 2 acyclic sulfur atoms being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, there being no more than one -SH on any single carbon atom of the heterocyclic ring, and all carbon-carbon bonds in the heterocyclic compound being single bonds.

13. A composition consisting essentially of ortho-anisidine and from about 0.01% to about 0.5% of thiazoline-2-thiol.

14. A composition consisting essentially of orthoanisidine and from about 0.01% to about 0.5% of 1,3A-thiadiazole-2,5-dithiol.

15. A composition consisting essentially of an aromatic amine of the formula RNI-I2 in which R is a di-substituted phenyl radical in which one substituent is a methoxy group in one of the positions ortho and para to the NH2 group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of a member of the group consisting of heterocyclic compounds and their zinc salts in which each heterocyclic compound contains 2 to 10 carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of 5 to 6 atoms of which 2 to 4 atoms are carbon atoms and 2 to 3 atoms are heterocyclic atoms selected from the group consisting of sulfur and nitrogen atoms, not more than 2 of such heterocyclic atoms being alike, the substituents on all heterocyclic nitrogen atoms "being restricted to hydrogen atoms and a single methyl group, and the substituents on each carbon atom of the heterocyclic ring being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbon radicals, -SH and =3, there being no more than one saturated hydrocarbon radical or Sl-I on any single carbon atom of the heterocyclic ring.

16. A composition consisting essentially of an aromatic amine of the formula R-NH2 in which R is a (ii-substituted phenyl radical in which one substituent is a methoxy group in one of the positions ortho and para to the NHz group and the other substituent is a, methyl group, and from about 0.01 to about 0.5% of a heterocyclic compound which contains 2 to 10 carbon atoms, 1 to 3 sulfur atoms, at least 2 hydrogen atoms and a single heterocyclic ring composed of 5 to 6 atoms of which 2 to l atoms are carbon atoms and 2 to 3 atoms are heterocyclic atoms selected from the group consisting of sulfur and nitrogen atoms, not more than 2 of such heterocyclic atoms being alike, the substituents on all heterocyclic nitrogen atoms being restricted to hydrogen atoms and a single methyl group, and the substituents on the carbon atoms of the heterocyclic ring [being restricted to at least one member of the group consisting of hydrogen atoms, saturated hydrocarbon radicals, -SH and =S, there being no more than one saturated hydrocarbon radical or -SI-I on any single carbon atom of of the heterocyclic ring.

1'7. A composition consisting essentially of an aromatic amine of the formula R-NH2 in which R is a (ii-substituted phenyl radical in which one substituent is a methoxy group in one of the positions ortho and para to the N112 group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of a hetero-cyclic compound which consists of 2 to 10 carbon atoms, 1 to 2 heterocyclic nitrogen atoms, 2 to 3 sulfur atoms, and at least 2 hydrogen atoms and contains a single heterocyclic ring of 5 to 6 atoms composed of at least 2 carbon atoms, 1 to 2 nitrogen atoms and 1 to 2 sulfur atoms, the substituents on the nitrogen atoms being restricted to hydrogen atoms, each sulfur atom, other than those that are members of the heterocyclic ring, being bonded solely to both a hydrogen atom and a carbon atom which is a member of the heterocyclic ring, there being no more than one saturated hydrocarbon radical or Sl-I on any single carbon atom of the heterocyclic ring.

18. A composition consisting essentially of an aromatic amine of the formula RNH2 in which R is a (ii-substituted .phenyl radical in which one substituent is a methoxy group in one of the positions ortho and para to the NHz group and the other substituent is a methyl group, and from about 0.01% to about 0.5% of 1,3,4-thidiazole- 2,5-dithiol.

19. A composition consisting essentially of 2-methoxy-5-methyl-aniline and from about 0.01% to about 0.5% of 1,3,4-thiadiazole-2,5- dithiol.

No references cited. 

1. A COMPOSITION CONSISTING ESSENTIALLY OF AN AROMATIC AMINE OF THE FORMULA R-NH2 IN WHICH R IS A MEMBER OF THE GROUP CONSISTING OF MONOSUBSTITUTED PHENYL RADICALS IN WHICH THE SUBSTITUENT IS AN ALKOXY GROUP OF 1 TO 2 CARBON ATOMS IN ONE OF THE POSITIONS ORTHO AND PARA TO THE NH2 GROUP AND DISUBSTITUTED PHENYL RADICALS IN WHICH ONE SUBSTITUENT IS A METHOXY GROUP IN ONE OF THE POSITIONS ORTHO AND PARA TO THE NH2 GROUP AND THE OTHER SUBSTITUENT IS A METHYL GROUP, AND FROM ABOUT 0.01% TO ABOUT 0.5% OF A MEMBER OF THE GROUP CONSISTING OF HETEROCYCLIC COMPOUNDS AND THEIR ZINC SALTS IN WHICH EACH HETEROCYCLIC COMPOUND CONTAINS 2 TO 10 CARBON ATOMS, 1 TO 3 SULFUR ATOMS, AT LEAST 2 HYDROGEN ATOMS AND A SINGLE HETEROCYCLIC RING COMPOSED OF 5 TO 6 ATOMS OF WHICH 2 TO 4 ATOMS ARE CARBON ATOMS AND 2 TO 3 ATOMS ARE HETEROCYCLIC ATOMS SELECTED FROM THE GROUP CONSISTING OF SULFUR AND NITROGEN ATOMS, NOT MORE THAN 2 OF SUCH HETEROCYCLIC ATOMS BEING ALIKE, THE SUBSTITUENTS ON ALL HETEROCYCLIC NITROGEN ATOMS BEING RESTRICTED TO HYDROGEN ATOMS AND A SINGLE METHYL GROUP, AND THE SUBSTITUENTS ON EACH CARBON ATOM OF THE HETEROCYCLIC RING BEING RESTRICTED TO AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF HYDROGEN ATOMS, SATURATED HYDROCARBON RADICALS, -SH AND =S, THERE BEING NO MORE THAN ONE SATURATED HYDROCARBON RADICAL OR -SH ON ANY SINGLE CARBON ATOM OF THE HETEROCYCLIC RING. 